High efficiency is critical.

Stick with the Heresy's. I bought a pair to use with my SET amps: Sanei 560A 2A3 and Will Vincent 45. Also my SE 6BG6 custom build. They have sufficient sensitivity to work well even with the SE 45 (1.75 watts). Yes, bass response drops off below 50hz, but for most rock/jazz not a problem. For the rest I have a Carver sub.

You could get Khorns if you have a large enough room with two free corners. Or the Speakerlab version, to save money! Come to think of it, my Speakerlab 7's would probably work well with the Sanei 2A3 amp. They resemble a Heresy with an extra woofer on the bottom - no sub needed! Recommended!